1. Field of the Invention
The invention relates to a sheet processing apparatus which moves sheets successively stacked on a tray in a direction crossing a sheet discharging direction to thereby align the side edges of the sheets, and an image forming apparatus provided with the same.
2. Description of the Related Art
There has heretofore been a sheet processing apparatus which moves sheets one by one on a tray in a direction crossing a sheet discharging direction by a cross-directionally moving member to thereby abut one side edge of the sheet against a cross-side restricting member and align the side edge (side edge alignment) (Japanese Patent Application Laid-open No. H8-67400). The side edge refers to that edge of the sheet which is along the sheet discharging direction.
The standby position of the cross-directionally moving member is coincident with the center of the sheet discharged to the tray in the width direction thereof. Therefore, the cross-directionally moving member is adapted to contact with the central portion of the sheet in the width direction thereof to thereby move the sheet in the width direction thereof and abut it against the cross-side restricting member.
Also, the sheet processing apparatus is adapted to be provided, for example, in the apparatus main body of an image forming apparatus for forming an image on a sheet, and effect the side edge alignment of the sheet on which an image has been formed and which has been discharged from the apparatus main body.
Further, the sheet processing apparatus is adapted to abut a sheet against the cross-side restricting member at a substantially constant speed to thereby effect side edge alignment.
However, the cross-directionally moving member of the conventional sheet processing apparatus, when it moves a succeeding sheet on a preceding sheet to thereby abut one side edge of the succeeding sheet against the cross-side restricting member, has sometimes slidden relative to the succeeding sheet because the cross-directionally moving member sides onto the other side edge of the preceding sheet through the succeeding sheet. Particularly, when the side edge portion of the preceding sheet is upwardly curled, the cross-directionally moving member has sometimes slidden on the succeeding sheet.
Therefore, the sheet processing apparatus has sometimes been incapable of reliably align the side edge of the succeeding sheet. Also, when the cross-directionally moving member rides onto the other side edge of the preceding sheet through the succeeding sheet, it has sometimes disturbed the alignment of the preceding sheet.
Further, there has been the problem that a sheet bundle thus subjected to a disturbed side edge aligning process, when subjected to post-processing such as stapling, becomes a poor-looking sheet bundle.
Also, the conventional sheet processing apparatus is adapted to abut a sheet against the cross-side restricting member at a substantially constant movement speed to thereby effect side edge alignment and therefore, the cross-directionally moving member has sometimes wrinkled the side edge portion of the sheet, and the sheet has sometimes been rebounded by the reaction resulting from the abutting. For this reason, in the conventional sheet processing apparatus, it has been difficult for the sheet to be reliably abutted against the cross-side restricting member without the side edge portion thereof being wrinkled and without being rebounded. Particularly, when the side edge of the sheet remains incapable of being aligned and thereafter, post-processing such as binding a sheet bundle is performed, there has arisen the problem that the sheet bundle becomes a poor-looking sheet bundle of which the side edges are not uniform.
Also, an image forming apparatus provided with a sheet processing apparatus poor in its side edge aligning performance cannot smoothly feed sheets into the sheet processing apparatus and therefore, has been incapable of enhancing its image forming efficiency.